1. Field of the Invention
The present invention relates to a high average power laser system and more particularly to a modular high average power laser system which includes a phased array of parallel power amplifiers, connected to a common master oscillator for synthesizing composite beams of varying power levels, and adaptive optics which include spatial light modulators for encoding the wave front of the laser beam with a conjugate phase to compensate for atmospheric aberrations.
2. Description of the Prior Art
High power laser weapon systems are generally known in the art. An example of such a high power laser system is disclosed in U.S. Pat. No. 5,198,607, assigned to the same assignee as the assignee of the present invention and hereby incorporated by reference. Such laser weapon systems normally include a tracking system for locking the high power laser on a target, such as a ballistic missile, cruise missile, bomber or the like. Such laser weapons are used to destroy or "kill" such targets. The effectiveness of such a laser weapon system depends on many factors including the power of the laser at the target. Many factors are known to affect the power of the laser at the target. One such factor is known as thermal blooming, discussed in detail in U.S. Pat. No. 5,198,607. In order to compensate for thermal blooming, it is known to use multiple high power lasers for killing a single target, for example as disclosed in U.S. patent application Ser. No. 08/729,108, filed on Oct. 11, 1996 for a LASER ALONG BODY TRACKER (SABOT) by Peter M. Livingston, assigned to the same assignee as the assignee of the present invention.
Other factors are known to affect the power level of the laser at the target including atmospheric aberrations which cause distortion of the wave front of the high power laser beam. In order to correct the wave front of the laser beam due, for example, to atmospheric aberrations, various adaptive optics systems have been developed. Examples of such systems are disclosed in U.S. Pat. Nos. 4,005,935; 4,145,671; 4,233,571; 4,399,356; 4,500,855; 4,673,257; 4,725,138; 4,734,911; 4,737,621; 4,794,344; 4,812,639; 4,854,677; 4,921,335; 4,996,412; 5,164,578; 5,349,432; 5,396,364; 5,535,049; and 5,629,765, all hereby incorporated by reference.
Various laser wave front compensation techniques have been employed. For example, U.S. Pat. Nos. 4,005,935; 4,794,344; and 5,535,049 utilize Brilloin scattering techniques to generate a phase conjugate of the laser wave front in order to compensate for distortions. Other techniques include the use of spatial light modulators which divide the laser beam into a plurality of subapertures, which, in turn, are directed to an array of detectors for detecting the phase front distortion which, in turn is used to compensate the phase fronts as a function of the distortion. Examples of systems utilizing spatial light modulators are disclosed in U.S. Pat. Nos. 4,399,356; 4,854,677; 4,725,138; 4,737,621; and 5,164,578, all hereby incorporated by reference.
There are several disadvantages of the systems mentioned above. One disadvantage relates to the fact that such laser systems have a fixed architecture for a given laser power output level. As such, such laser systems are generally not scalable. Unfortunately, various laser applications require different power levels. For example, laser weapon applications require different output power levels depending on the type and distance of the intended targets. In such laser weapon applications, separate laser systems are required for each application which increases the cost of the laser weapon system as well as the number of spare parts required for maintenance.
Another disadvantage of such known laser systems with phase front compensation is that such systems are limited to the power level ability of the various components forming the system. For example, such laser weapon systems are known to use lasers, normally high average power chemical lasers which have power levels of a few kilowatts. Due to such high power requirements, spatial light modulators have heretofore been unsuitable for such applications. As such, alternate techniques have been developed providing wave front compensation of such high average power lasers. For example, U.S. Pat. No. 4,321,550 relates to a high average power laser system with phase conjugate correction. In this system, the phase front correction is based on Brilloin scattering. U.S. Pat. No. 3,857,356 discloses another system which utilizes a diffraction grating to provide a reduced power level with test beam. The system disclosed in '636 Patent also includes an interferometer with a phase shifting device disposed in one leg to provide phase front compensation high average power laser systems.
Although such systems are suitable for providing phase front compensation of high average power laser systems, such systems are relatively bulky and inefficient. In many applications, there is a desire to use laser weapons that are more efficient and compact, particularly for laser weapon systems.